Additional colorspace clarification

Note that SDL_MATRIX_COEFFICIENTS_BT470BG is functionally equivalent to SDL_MATRIX_COEFFICIENTS_BT601

src/render/metal/SDL_render_metal.m

@@ -590,6 +590,7 @@ size_t GetYCbCRtoRGBConversionMatrix(SDL_Colorspace colorspace, int w, int h, in
     const int YUV_SD_THRESHOLD = 576;
 
     switch (SDL_COLORSPACEMATRIX(colorspace)) {
+    case SDL_MATRIX_COEFFICIENTS_BT470BG:
     case SDL_MATRIX_COEFFICIENTS_BT601:
         return GetBT601ConversionMatrix(colorspace);
 

src/render/vulkan/SDL_render_vulkan.c

@@ -2505,6 +2505,7 @@ static int VULKAN_CreateTexture(SDL_Renderer *renderer, SDL_Texture *texture, SD
         /* Create samplerYcbcrConversion which will be used on the VkImageView and VkSampler */
         samplerYcbcrConversionCreateInfo.format = textureFormat;
         switch (SDL_COLORSPACEMATRIX(texture->colorspace)) {
+        case SDL_MATRIX_COEFFICIENTS_BT470BG:
         case SDL_MATRIX_COEFFICIENTS_BT601:
             samplerYcbcrConversionCreateInfo.ycbcrModel = VK_SAMPLER_YCBCR_MODEL_CONVERSION_YCBCR_601_KHR;
             break;